Overload relay



April 22, 1958 J. B. RAMSEY 7 ET AL OVERLOAD RELAY Filed April 6, 1955 S M 50 Y T mm E N 0G N nnd R v n 0 N l s an A mu n? J d 7 ,n x 2 O. W a 2 n 3 rlll fir w M Q 3 5 4 3 6 3 O 4 A .W F

WITNESSES'. 471

UnitedStates Patent O OVERLOAD RELAY James B. Ramsey and Paul T. Anderson, Chippewa Township, Beaver County, Pa., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pen, 3 corporation of Pennsylvania Application April 6, 1955, Serial No. 499,629

15 Claims. (Cl. 200113) Our invention relates to thermostatic devices, and more particularly to reset thermostatic overload relays for the protection of electric devices.

The electromagnetic contactors and line starters, for connecting and disconnecting electric motors, and other load units, from a source of electric power, usually inelude one or more thermostatic overload control relays. These relays are mounted on the base plate of the contactor and are for the purpose of protecting the motor, or other load unit, against overloads.

The trend in the electric industry is to make these electromagnetic contactors smaller and smaller and cheaper and cheaper with respect to their ratings without the sacrifice of any reliability and efficiency. It thus becomes highly desirable to have an overload control relay which can be used with such smaller contactors without being disproportionately large and expensive, and without sacrifice in reliability and efiiciency.

One broad object of our invention is to provide a thermal overload control relay that shall be eflicient and reliable in operation, economical'to manufacture, and

shall be small in size and be easily installed.

One other broad object of our invention is the provision, in a thermal overload control relay, of novel resetting means for the relay after such relay has operated by reason of an overload.

It is also an object of our invention to provide an overload control relay having, relative to prior art devices, a quite short tripping time. g

It is a somewhat more specific object of our invention to provide, in a thermal overload control relay, for adjusting the tripping time from a relatively very short time interval to a considerably greater time interval.

Another specific object of our invention is the provision of a trip free relay, that is, a relay that trips on overload even though the manual resetting element is actuated.

The objects stated are merely illustrative. Other objects and advantages of our invention will become more apparent from a study of the following specification and the accompanying drawing, in which:

Figure 1 is a plan view of our thermal overload'control relay;

Fig. 2 is a vertical sectional view, on line IIII of Fig. 1, showing the essential elements of the relay as seen from the side and in position on the insulating base;

Fig. 3 is a plan view of the load circuit through the relay; and

Fig. 4 is a side view of the showing in Fig. 3.

For a better understanding of the objects of our invention, it is to be noted that in the cases where electric motors are used to drive refrigerating apparatus, air

conditioning apparatus, pumps, etc-apparatus likely to overload the motors-and wherein the operation of such motors may be controlled by an overload relay, it is nec-' essar'y, when the overload relay operates to stop the motor in case of an overload, that the overload relay renain in the operated, or tripped, position until manually reset in order to prevent the restarting of the motor. Restarting of the motor would normally occur were the overload relay to automatically return to the non-operated, or re-set position. Our invention provides for tripping of the overload relay and no automatic re-set where such operation is desired. To restart the motor the overload relay has to be re-set by hand.

In many installations automatic restarting of the motor is desirable, provided the time interval between tripping of the overload relay and its automatic operation to a re-set position is of the desired length. Our invention provides for the adjustment of this time interval to the desired length and provides for automatic re-set opera: tion of the relay.

In the drawings the reference characters 1, 2, and 3 designate the three parts of the supporting base of the relay elements. The three parts areformed of insulating material such as hard rubber, melamine, or molding compounds, as polyester resins, or phenolic resins.

The part 1 carries the control circuit and may thus be designated the control base. The part 2 carries the load circuit and may thus be designated the load base. The part 3 carries some of the means for selecting the operative range of the re-set bar and may thus be designated the re-set base.

The control circuit comprises the terminal 4, silvered spring plate contact 5, silver contact 6 on the pre-stressed spring 7 and terminal 8.

The terminal 4 is bent back upon itself, as shown at the left, so connections can be made in crowded quarters from above. The terminal is riveted into the control base by rivet 13, as shown. The rivet 13 also secures the silvered spring contact 5. This contact 5, when not engaged by the silver contact 6 on the pre-stressed spring 7, is displaced counterclockwise at the right by a small angle above the horizontal projection of the terminal 4 to the right of rivet 13. When contact 6 upon its downward movement engages contact 5 and depresses it against the right hand projection of terminal 4 a slight wiping action takes place to provide a good contact. Further, the spring etfect of the contacts 5 and 6 and thewiping action provide a damping efiect to thus prevent contact bouncing during operation and by reason of vibration of the relay.

The pro-stressed spring 7 is'preferably made of springlike bronze. The spring has a gable-shaped left end carrying the contact 6. The mid region is provided with a transverse opening through which the bolt 9 passes. Bolt 9 holds control base 1 rigidly on the load base 2. The opening in the spring for the bolt 9 is quite ample in size so that the operative movements of the spring are in nowise affected by the presence of the bolt.

The right end of the spring '7 is trifurcate with the center time 10 shorter than the two outer tines. The outer tines pass under the H-shaped crosspiece 11. The left legs of the crosspiece lie flat on the top surface of the outer tines and the right legs are bent in a U-shaped manner. to engage the outer edges of the outer tines and the outer edges of terminal 8. 7 piece 11 and the outer tines are riveted to the control base 1 by rivet 14 as shown. p

The spring 7 is pre-stressed so that when a downward force of suflicient magnitude is applied to the tine 10 the spring will cause the left end of the spring to move clockwise with a snap action to open the circuit at contacts 5 and 6. When the left end is moved counterclockwise by the re-set bar 12 the spring will re-set to the position shown with a snap action.

The downward movement of the re-set bar 12 is limited by the molded cylindrical upward projection 15 formed integral with the control base 1. The length of The H -shaped crossthe projection is so chosen that spring 7 moves counterclockwise with a snap action when the bottom of bar 12 is on the top of the projection, or stop, 15, provided the downward force on the tine 10 is no longer acting.

The load circuit includes terminal 16, spring 19, hearing 20, adjusting bolt 21, bimetallic element 22, resist ance strip 23, copper cable 24 and terminal 27.

Terminal 16 is U-shaped with leg 17 projecting away from the observer, bight 28 nearer the observer and leg 18 projecting away from the observer. Leg 18 rigidly secured thereto carries the spring 19 and the bearing 20. Spring 19 is U-shaped. The upper leg is rigidly secured, as by soldering, or brazing, to the left end of the bimetal strap 22. Both the strap 22 and spring 19 have threaded engagement with the adjusting bolt 21. Terminal 16 is rigidly secured to the control base by the bolt, or rivet, 29.

The resistance strip 23 is rigidly secured, as by brazing, at its right end to the right end of bimetal 22. At

the left end of strip 23 the left end of the woven copper cable 24 is secured as by brazing at 25. The cable 24 is not under tension between point 25 and its brazed con nection at point 26 to terminal 27, but it does not have excess length so that it does not rest on strap 23 nor contact the sides of the base 2. Cable 24 thus does not affectthe operation of the actuating parts of the relay.

A better understanding of the structural merits of our overload relay and its functional characteristics may be had from a study of our relay in simplified control and load circuits. In Fig. 2, leads 100 and 105 designate the source of electric energy for the motor M. The accelerating controller 110 for the motor is shown in block form since none of the elements in the controller form part of our invention. 7

If the motor M is to be started, the starting switch 101 is depressed, whereupon a circuit is established from lead 100 through starting switch 101, actuating coil 102 of control contactor 103, terminal 4, contacts 5 and 6, spring 7, terminal 8, stop switch 104 to supply lead 105. Contactor 103 thus operates to close contacts 106 and 107. The closure of contacts 106 shunts starting switch 101 to thus establish a holding circuit for contactor 103. The closure of contacts 107 establishes the load circuit from lead 100 through contacts 107, shunt 108, conductor 109, starting controller 110, and motor M to lead 105. Another branch of the load circuit is established from contacts Hi7 through terminal 16, parts 18, 19, and 21, bimetal strap 22, resistance member 23, cable 24, and terminal 27 to conductor 109. This second branch of the load circuit just traced may have its proportion of load current adjusted by the shunt 108. In any event the current traversed by the bimetal 22 and the resistance heater 23 is a function of the load current of the motor M. It the motor carries an overload, contacts 5 and 6 are disengaged and the motor is stopped.

It will be noted, for the particular showing made, that the bimetal is connected directly in one branch of the load circuit. The very minimum time is thus rcqu-ired for it to be actuated when an overload flows in the circuit.

The resistance strip 23, connected in series with the bimetal 22, is an electric heater element disposed to heat the bimetal 22. The total heating effect on the bimetal strap 22 is thus determined by the direct heating produced by the current in the bimetal strap itself and the indirect heating produced by the resistance element.

The tripping time of the relay may readily be adjusted by shifting the point of connection toward the right to include less and less of the resistance element in the load circuit. The longest time element may, of course, be obtained by connecting resistance element directly across the terminals 16 and 27. This connection would eliminate the bimetal strap 22 entirely from the load circuit and provides indirect heating only. The time limit adjustment between the two limits above discussed 4 may thus be varied by suitable changes in the connection of the parts 16, 22, 23, 24, and 27 to alter the ratio of direct heating to indirect heating of the bimetal strap 22.

The terminal 27 is Z-shaped as shown and is secured to load base 2 by the bolt 30. A hole is provided in the lower leg of terminal 27. This hole registers with an elongated bearing hole in the load base 2 for receiving the plunger 31 for actuating spring 7. The plunger 31 is made of insulating material and is disposed in its bearing opening so that its upper end is in operative position under the right end of the bimetal 22 and its lower end rests on the right end of tine 10.

When the bimetal is heated by an overload its right end swings down or clockwise, to exert longitudinal pressure on plunger 31. When the force gets great enough spring 7 is caused to break the contact at terminals 5 and 6 with a snap action.

The re-set base 3 comprises a flat piece of insulating material, preferably of the same material as the material of the control base 1 and load base 2.

Terminal 27 is undercut a small amount at the top to receive the two end projections 32 and 33, as shown. The left end of re-set base extends under leg 17 of terminal 16. The load base 2 is provided with side ledges upon which the base 3 rests.

The load base 2 is provided with a lug 34 which together with the recessed rear edge 35 of re-set base 3 form an upper bearing for the re-set bar 12. A spring 36, shaped as shown, is riveted at 37 to the re-set base 3. The rivet is not so tight as to prevent movement of the spring 36 about the rivet 37 as a pivot. The right end of spring 37 is provided with detent 38 to fit into the hole 39 when the spring 36 is in the position shown in Figs. 1 and 2.

The left end of spring 36 is provided with a projection 40 for selective insertion in the holes 41 or 42 in the reset bar 12. When the reset bar 12 is in the position shown in Fig. 2 and projection 40 is in opening 41, then the end marked with the H is projecting from the base. This means the bottom end of bar 12 is in the position shown in Fig. 2 and when an overload actuates the spring 7 it will snap into clockwise position and stay there. When the bimetal has cooled sufficiently to release plunger 31, then any time thereafter the re-set bar 12 may be depressed to re-set the overload relay.

When it is desired to make the relay automatic re-set, then spring 36 is first moved counterclockwise (see Fig. l) sufliciently to withdraw projection 40 from opening 41. The re-set bar 12 is then changed end for end so that the A appears right-side-up at the outside of the base. The spring 36 is now moved clockwise so that projection 40 now is inserted in the opening 42. The bottom of the re-set bar 12 will now rest on projection 15. Now when the bimetal acts on plunger 31 the contacts at 5 and 6 are broken, i. e., the control circuit is opened and stays open as long as bimetal 22 holds plunger 31 down. The moment the bimetal has cooled sufliciently, the control circuit is again closed and starting of the motor is attempted. In short, the relay re-sets automatically. The exposed A means just that, namely, the relay functions on automatic re-set.

The particular feature just discussed also makes the overload relay trip free. The terminology trip free in the trade means that even though the reset rod 12 is held down in the hand resetting position the relay is still free to trip on an overload and open the control circuit. The load unit, as the motor M, thus can not be run under overload conditions by holding the manual reset rod down.

The spring 19 is so shaped when unstressed that, in the absence of bolt 21, the right end of the bimetal strip will be the very maximum distance away from plunger 31, as shown in Fig. 4. This means that when bolt 21 is inserted in the threaded junction of spring 19 and bimetal 22' in such manner as to contact the bearing with substantially no pressure, then the overload relay is adjusted for its maximum tripping temperature of the relay. The current carrying rating of the relay may thus be changed by movement of bolt 21. By proper adjustment of bolt 21 the spacing between the rightend of the bimetal and plunger 31 may be made as small as may be desired. The tripping time, for a particular constant overload current, may thus also be changed by bolt 21. In fact, the adjustment may be such as to place the right end of bimetal 22 very near plunger 31 to make the current rating extremely short. While the elements 18, 19, 20,- and 21 are primarily for the purpose of changing the current carrying rating of the relay, some time adjustment is also obtained.

From the disclosure made, it is apparent that our overload relay is very simple in structure, consisting of few and simple elements that are easily manufactured and readily assembled.

Further, our overload relay is small and compact. The showing in the drawing is actually to double scale. The volume of our overload relay is just a trifle less than 42% of the volume of a generally similarly dimensioned and like rated overload relay now in extensive use.

While we have disclosed but one embodiment of our 7 invention it is, of course, understood that the invention is capable of modifications that fall within the spirit and scope of our invention.

We claim as our invention:

1. In an electric control device, in combination, an elongated base of insulating material, a first electric terminal secured to the left end of the base, a bimetallic strap at its left end secured to the first terminal and its right end free to swing through an are upon heating of the bimetallic strap, a second terminal secured to the base adjacent the right end of the bimetallic strap, a fiexible electric connection between the right end of the bimetallic strap and the second terminal, whereby the bimetallic strap at its right end is caused toswing clockwise in the event of a load current of a selected value passing between the two terminals, a third terminal secured to the left end of the base, a fourth terminal secured to the right end of the base, a pre-stressed elongated conducting spring at its right end secured to the fourth terminal and at its left end normally engaging the third terminal, an elongated plunger of insulating .ma-

terial mounted in the base for free longitudinal movement, one end of the plunger being disposed in operative relation to the right end of the bimetallic strap and the other end of the plunger being in operative relation to the pre-stressed spring so that actuation of the spring by the plunger effects disengagement of theleft end of the spring from the third terminal with a snap action.

2. In an electric control device, in combination, a base of insulating material having mounted therein in insulated relation a portion of a first, or load current carrying circuit and a second, namely a control current carrying circuit, said first circuit including a first terminal, a bimetal strap at one end secured to the first terminal, and a flexible lead connecting the free end of the bimetal to a second terminal, the second circuit including a third terminal, an elongated pre-stressed spring having a contact at one end that either engages thethird terminal or disengages the third terminal with a snap action upon actuation of the spring at a selected point between its ends, and a fourth terminal to which the other end of the spring is attached, and a longitudinally operable plunger disposed between the free end of the bimetal strap and the selected point on the spring, whereby deflection of the free end of the bimetal strap actuates the pre-stressed spring.

3. In an electric control device,'in combination, a base of insulating material having mounted therein in in sulated relation a portion of a first, or load current'carrying circuit and a second, namely a control current carry- 6 ing circuit, said first circuit including a first terminal, a bimetal strap at one end secured to the first terminal, and a flexible lead connecting the free end of the bimetal to a second terminal, the second circuit including a third terminal, an elongated pro-stressed spring having a contact at one end that either engages the third terminal or disengages the third terminal with a snap action upon actuation of the spring at a selected point between its ends, and a fourth terminal to which the other end of the spring is attached, a longitudinally operable plunger disposed between the free end of the bimetal strap and the selected point on the spring, whereby deflection of the free end of the bimetal strap actuates the pre-stressed spring, means for adjusting the initial spacing between the end of the plunger and the free end of the bimetal straps, and means for resetting the prestressed spring after it has been actuated.

4. A thermostatic overload relay, comprising, a base of insulating material, a load circuit including a first terminal and a second terminal, a bimetal strap being at one end, through connecting means, rigidly connected to the first terminal and through a flexible lead connected to the second terminal, whereby the end of the bimetal strap flexibly connected to the second terminal is free to move through an arc depending on the load current flowing from the first terminal to the second terminal, a snap acting switch mounted in the base, a plunger of insulating material mounted in the base for longitudinal movement, one end of the plunger being disposed adjacent the free end of the bimetal strap and the other end being disposed adjacent the snap acting switch, whereby deflection of the bimetal strap actuates the snap acting switch.

5. A thermostatic overload relay, comprising, a base of insulating material, a load circuit including a first terminal and a second terminal, a bimetal strap being at one end, through connecting means, rigidly connected to the first terminal and through a flexible lead connected to the I second terminal, whereby the end of the bimetal strap flexibly connected to the second terminal is free to move through'an arc depending on the load current flowing from the first terminal to the second terminal, a snap acting switch mounted in the base, a plunger of insulating material mounted in the base for longitudinal movement, one end of the plunger being disposed adjacent the free end of the bimetal strap and the other end being disposed adjacent the snap acting switch, whereby defiection of the bimetal strap actuates the snap acting switch, and means for adjusting the tripping time of the overload relay. I

6. A thermostatic overload relay, comprising, a base of insulating material, a load circuit including a first terminal and a second terminal, a bimetal strap being at one end, through connecting means, rigidly connected to the first terminal and through a flexible lead connected to the second terminal, whereby the end of the bimetal strap flexibly connected to the second terminal is free to move through an arc depending on the load current flowing fromthe firstterminal to the second terminal, a snap acting switch mounted in the base, a plunger of insulating material mounted in the base for longitudinal movement, one end of the plunger being disposed adjacent the free end of. the bimetal strap and the other end being disposed adjacent the snap acting switch, whereby deflection of the bimetal strap actuates the snap acting switch,

said outside tines being rigidly secured to the second terminal with the spring being so pre-stressed that depression of the middle tine will cause the spring to move overcenter with a snap action to control the circuit connection between the first terminal and the contact on the spring, a directly heated bimetal element in a load circuit adapted to deflect as a function of the load current traversing the bimetal element, operating means operatively interconnecting the middle tine with the movable portion of the bimetal element to actuate the prestressed spring, and spring resetting means in the base coacting with the end of the spring carrying the contact to reset it to its original position after having been actuated by the bimetal element.

8. A thermostatic overload relay, in combination, a base of insulating material, a first terminal fixed in the base, a second terminal spaced from the first also fixed in the base, a pre-stressed conducting spring carrying a contact at one end and being trifurcate at the other end, the two outside tines of the furcate end being somewhat longer than the middle tine, said outside tines being rigidly connected to the second terminal with the spring being so pre-stressed that when the middle tine lies above the plane of the outside tines the contact on the spring engages the first terminal but when the middle tine is depressed the spring snaps overcenter to break the circuit between the contact and first terminal with a snap action, a directly heated bimetal element, interconnected with the load circuit to be protected against overloads, having a portion that deflects as a function of load current, operating means operatively interconnecting the middle tine with the movable portion of the bimetal element to actuate the pre-stressed spring, and means for adjusting the initial spacing between the movable portion of the bimetal element and the operating means to adjust the trip ping time of the overload relay, and spring resetting means in the base coacting with the end of the spring carrying the contact to reset it to its original position after the bimetal element has cooled after having been actuated by the bimetal element.

9. A thermostatic overload relay, in combination, a base of insulating material, a first terminal fixed in the base, a second terminal spaced from the first also fixed in the base, a pre-stressed conducting spring carrying a contact at one end and being trifurcate at the other end, the two outside tines of the furcate end being somewhat longer than the middle tine, said outside tines being rigidly connected to the second terminal with the spring being so pre-stressed that when the middle tine lies above the plane of the outside tines the contact on the spring engages the first terminal but when themiddle tine is depressed the spring snaps overcenter to break the circuit between the contact and first terminal with a snap action, a directly heated bimetal element, interconnected with the load circuit to be protected against overloads, having a 5;

portion that deflects as a function of load current, operating means operatively interconnecting the middle tine with the movable portion of the bimetal element to actuate the pre-stressed spring, and means for adjusting the initial spacing between the movable portion of the bimetal element and the operating means to adjust the tripping time of the overload relay, spring resetting means in the base coacting with the end of the spring carrying the contact to reset it to its original position after the bimetal element has cooled after having been actuated by the bimetal element, said spring resetting means comprising an elongated push-rod mounted for longitudinal movement in the base projecting from the base so that the pushrod may be manually actuated.

10. A thermostatic overload relay, in combination, a base of insulating material, a first terminal fixed in the base, a second terminal spaced from the first also fixed in the base, a pre-stressed conducting spring carrying a contact at one end and being trifurcate at the other end, the two outside tines of the furcate end being somewhat longer than the middle tine, said outside tines being rigidly connected to the second terminal with the spring being so pre-stressed that when the middle tine lies above the plane of the outside tines the contact on the spring engages the first terminal but when the middle tine is .depressed the spring snaps overcenter to break the circuit between the contact and first terminal with a snap action, a directly heated bimetal element, interconnected with the load circuit to be protected against overloads, having a portion that deflects as a function of load current operating means operatively interconnectingthe middle tine with the movable portion ofthe bimetal element to actuate the pre-stressed spring, and means for adjusting the initial spacing between the movable portion of the bimetal element and the operating means to adjust the tripping time of the overload relay, spring resetting means in the base coating with the end of the spring carrying the contact to reset it to its original positionafter the bimetal element has cooled after having been actuated by the bimetal element, said spring resetting means comprising an elongated push-rod mounted for longitudinal movement in the base projecting from the base so that the pushrod may be manually actuated, and a. stop adjacent the spring for limiting the movement of the push-rod in the resetting direction, the position of the stop being so chosen that the spring is moved just suflicient to efiect snap action like resetting after the action of the bimetal element ceases but prevents bending of the spring in the event excessive resetting force is applied to the push-rod,

11. A thermostatic overload relay, in combination, a base of insulating material, a first terminal fixed in the base, a second terminal spaced from the first also fixed in the base, a pre-stressed conducting spring carrying a contact at one end and being trifurcate at the other end, the two outside tines of the furcate end being somewhat longer than the middle tine, said outside tines being rigidly connected to the second terminal with the spring being so pre-stressed that when the middle tine lies above the plane of the outside tines the contact on the spring engages the first terminal but when the middle tine is depressed the spring snaps overcenter to break the circuit between the contact and first terminal with a snap action, a directly heated bimetal element, interconnected with the load circuit to be protected against overloads, having a portion that deflects as a function of load current, operating means operatively interconnecting the middle tine with the movable portion of the bimetal element to actuate the pro-stressed spring, and means for adjusting the initial spacing between the movable portion of the bimetal element and the operating means to adjust the tripping time of the overload relay, spring resetting means in the base coating with the end of the spring carrying the contact to reset it to its original position after the bimetal element has cooled after having been actuated by the bimetal ele-. ment, said spring resetting means comprising an elongated push-rod mounted for longitudinal movement in the base projecting from the base so that the push-rod may be manually actuated, a stop adjacent the spring for limiting the movement of the push-rod in the resetting direction,- the position of the stop being so chosen that the spring is moved just suflicient to eflect snap action like resetting after the action of the bimetal element ceases but prevents bending of the spring in the event excessive resetting force is applied to the push-rod, and means for selectively biasing the push-rod either against the stop to provide for automatic reset operation of the overload relay or biasing the push-rod to a position spaced from the stop to provide for manual reset operation of the overload relay.

12. A thermostatic overload relay, in combination, a base ofinsulating material, a first terminal fixed in the base, a second terminal spaced from the first also fixed in the base, a pre-stressed conducting spring carrying a contact at one end and being trifurcate at the other end, thetwo outside tines of the furcate end being somewhat a if longer than the middle tine, said'outside tines being rigidly connected to the second terminal with the spring being so pre-stressed that when the middle tine lies above the plane of the outside tines the contact on the spring engages the first terminal but when the middle'tine is depressed the spring snaps overcenter to break the circuit between the contact and first terminal with a snap action, a directly heated bimetal element, interconnected with the load circuit to be protected against overloads, having a portion that deflects as a function of load current, operating means operatively interconnecting the middle tine with the movable portion of the bimetal element to actuate the pre stressed spring, and means for adjusting the initial spacing between the movable portion of the bimetal element and the operating means to adjust the tripping time of the overload relay, spring resetting means ,in the base coating with the end of the spring carrying the contact to reset it to its original position after the bimetal element has cooled after having been actuated by the bimetal element, said spring reset-ting means comprising an elongated push-rod mounted for longitudinal movement in the base projecting from thebase so that the spring for limiting the movementof the push-rod in the resettingdirection, the position of the stop being so chosen that the spring cannot be moved to the resetting position by the push-rod whereby resetting may be accomplished only after the action of the bimetal ceases to thus provide a trip free overload relay.

13. A thermostatic overload relay, in combination, a I

base of insulating material, a first terminal fixed in the base, a second terminal spaced from the first also fixed in the base, a pre-stressed conducting spring carrying a contact at one end and being trifurcate at the other end, the two outside tines of the furcate end being interconnected with the load circuit to be protected againstoverloads, having a portion that deflects as a function of load current, operating means operatively interconnecting the middle tine with the movable portion of the bimetal element to actuate the pre-stressed spring, and means for adjusting the initial spacing between the movable portion of the bimetal element and the operating means to adjust the tripping time of the overload relay, spring resetting means in the base coating with the end of the spring carrying the contact to reset it to its original position after the bimetal element has cooled after having been actuated by the bimetal element, said spring resetting means comprising anelongated push-rod mounted for longitudinal movement in the base projecting from the base so that the push-rod may be manuallyactuated,

the push-rod in the resetting direction, the position of v the push-rod may be manually actuated, a stop adjacent the stop being so chosen that the spring cannot be moved 10 either against the stop to provide for automatic reset operation of the overload relay or biasing the push-rod to a position spaced from the stop to provide for manual reset operation of the overload relay.

14. A thermostatic overload relay, comprising a base of insulating material, .a load circuit including a first terminal and a second terminal, a bimetal strap being at one end, through connecting means, substantially rigidly connectedto the first terminal and through a flexible lead connected to the second terminal, whereby the end of the bimetal strap llexibly connected to the second terminal is free to move through an arc depending on the load current flowing from the first terminal to the second terminal, a snap acting switch mounted in the base, a plunger of insulating material mounted in the base for longitudinal movement, one end of the plunger being disposed adjacent the free end of the bimetal strap and the other end being disposed adjacent the snap acting switch, where by deflection of the bimetal strap actuates the snap acting switch, said connecting means for the bimetal strap comprises a U-shaped relatively stitf spring member having one leg rigidly secured to the first terminal and the other leg rigidly secured to the bimetal strap, and means for adjusting the spacing between the legs of the U-shaped member to thus change the initial position of the free end of the'bimetal strap with reference to the plunger to thus adjust the tripping time of the overload relay.

15. A thermostatic overload relay, comprising a base of insulating material, a load circuit including a first terminal and a second terminal, a bimetal strap being at one end, through connecting means, substantially rigidly connected to the first terminal and through a flexible lead connected to'the second terminal, whereby the end of the bimetal strap flexibly connected to the second terminal is free to move through an arc depending on the load curleg rigidly secured to the bimetal strap, means for adjusting the spacing between the legs of the U-shaped member to thus change the initial position of the free end of the bimetal strap with reference to the plunger'to thus adjust thetripping final of the overload relay, and means for resetting the snap actingswitch after the bimetal strap has cooled.

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